Standard statistical methods often provide no way to make accurate estimates about the characteristics of hidden populations such as injection drug users, the homeless, and artists. In this paper, we further develop a sampling and estimation technique called respondent-driven sampling, which allows researchers to make asymptotically unbiased estimates about these hidden populations. The sample is selected with a snowball-type design that can be done more cheaply, quickly, and easily than other methods currently in use. Further, we can show that under certain specified (and quite general) conditions, our estimates for the percentage of the population with a specific trait are asymptotically unbiased. We further show that these estimates are asymptotically unbiased no matter how the seeds are selected. We conclude with a comparison of respondent-driven samples of jazz musicians in New York and San Francisco, with corresponding institutional samples of jazz musicians from these cities. The results show that ...

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Sampling and Estimation in Hidden Populations Using Respondent-Driven Sampling

Effective management of rare species, including endangered native species and recently introduced nonindigenous species, requires the detection of populations at low density. For endangered species, detecting the localized distribution makes it possible to identify and protect critical habitat to enhance survival or reproductive success. Similarly, early detection of an incipient invasion by a harmful species increases the feasibility of rapid responses to eradicate the species or contain its spread. Here we demonstrate the efficacy of environmental DNA (eDNA) as a detection tool in freshwater environments. Specifically, we delimit the invasion fronts of two species of Asian carps in Chicago, Illinois, USA area canals and waterways. Quantitative comparisons with traditional fisheries surveillance tools illustrate the greater sensitivity of eDNA and reveal that the risk of invasion to the Laurentian Great Lakes is imminent.

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“Sight‐unseen” detection of rare aquatic species using environmental DNA

Purpose – Public bodies are being encouraged to procure sustainably, to reduce their social and environmental footprint and in order to stimulate sustainability in the private sector. However, little is known about how public sector organisations internationally are responding to this encouragement or of the conditions that are most conducive to sustainable procurement (SP). The purpose of this paper is to address these gaps in our knowledge so as to inform policy development at the government and organisational levels.

Design/methodology/approach – The authors report the findings of a survey of SP practices within a sample of over 280 public procurement practitioners from 20 countries and with collective responsibility for expenditure totalling $45bn p.a.

Findings – The authors' analysis shows that some SP practices are evident in public sector procurement practice and that the extent and nature of SP practices varies significantly across regions. In addition, the authors highlight the main facilitators of, and barriers to, engagement with SP and investigate their importance for engagement with particular dimensions of SP.

Research limitations/implications – Survey respondents are volunteers and may to some degree be more interested in, or engaged with, SP than other public sector organisations. The analysis is cross-sectional and therefore provides only a snapshot of SP practice in the public sector organisations studied.

Practical implications – The paper identifies how policy and practice in SP vary across regions, providing practical insights into whether and how government policies are being implemented around the world.

Originality/value – The paper provides the first systematic and comprehensive insight into how public bodies are implementing SP internationally and of the major situational factors that are shaping engagement with SP. The authors evaluate the current effectiveness of policy initiatives regarding SP and highlight the organisational catalysts and inhibitors of greater involvement in SP.

Design/methodology/approach – The authors report the findings of a survey of SP practices within a sample of over 280 public procurement practitioners from 20 countries and with collective responsibility for expenditure totalling $45bn p.a.

Findings – The authors' analysis shows that some SP practices are evident in public sector procurement practice and that the extent and nature of SP practices varies significantly across regions. In addition, the authors highlight the main facilitators of, and barriers to, engagement with SP and investigate their importance for engagement with particular dimensions of SP.

Research limitations/implications – Survey respondents are volunteers and may to some degree be more interested in, or engaged with, SP than other public sector organisations. The analysis is cross-sectional and therefore provides only a snapshot of SP practice in the public sector organisations studied.

Practical implications – The paper identifies how policy and practice in SP vary across regions, providing practical insights into whether and how government policies are being implemented around the world.

Originality/value – The paper provides the first systematic and comprehensive insight into how public bodies are implementing SP internationally and of the major situational factors that are shaping engagement with SP. The authors evaluate the current effectiveness of policy initiatives regarding SP and highlight the organisational catalysts and inhibitors of greater involvement in SP.

Sustainable procurement in the public sector: an international comparative study

Foundations. J.J. Hox, E.D. de Leeuw, D. Dillman, The Cornerstones of Survey Research. N. Schwarz, B. Knauper, D. Oyserman, C. Stich, The Psychology of Asking Questions. P. Lynn, The Problem of Nonresponse. J. A. Harkness, Comparative Survey Research: Goal and Challenges. E. Singer, Ethical Issues in Surveys. Design. S.L. Lohr, Coverage and Sampling. E.D. de Leeuw, Choosing the Method of Data Collection. F.J. Fowler, C. Cosenza, Writing Effective Questions. D.A. Dillman, The Logic and Psychology of Constructing Questionnaires. P. Campanelli, Testing Survey Questions. Implementation. G. Loosveldt, Face-to-Face interviews. C. Steeh, Telephone Surveys. E.D. de Leeuw, J.J. Hox, Self-Administered Questionnaires: Mail Surveys and Other Applications. K.L. Manfreda, V. Vehovar, Internet Surveys. D.M. Steiger, B. Conroy, IVR: Interactive Voice Response. E.D. de Leeuw, D.A. Dillman, J.J. Hox, Mixed Mode Surveys: When and Why. Data Analysis. P.P. Biemer, S.L. Christ, Weighting Survey Data. L.M. Stapleton, Analysis of Data from Complex Surveys. S. Rassler, D.B. Rubin, N. Schenker, Incomplete Data: Diagnosis, imputation, and estimation. J.J. Hox, Accommodating Measurement Errors. Special Issues. P. Mohler, B. Pennell, F. Hubbard, Survey documentation: Towards Professional Knowledge Management in Sample Surveys. L.E. Lyberg, P.P. Biemer, Quality Assurance and Quality Control in Surveys. J.T. Lessler, J. Eyerman, K. Wang, Interviewer Training. G. Lensvelt-Mulders, Surveying Sensitive Topics. D. Sikkel, A. Hoogendoorn, Panel Surveys. J. Betlehem, Surveys Without Questions.

International handbook of survey methodology.

The theoretical and empirical literature generally regards international migration as producing a cycle of dependency and stunted development in sending communities. Most migrants' earnings are spent on consumption; few funds are channeled into productive investment. We argue that this view is misleading because it ignores the conditions under which productive investment is likely to be possible and profitable. We analyze the determinants of migrants' savings and remittance decisions, using variables defined at the individual, household, community, and macroeconomic levels. We identify the conditions under which U.S. earnings are repatriated to Mexico as remittances and savings, and indicate the factors leading to their productive investment.

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International Migration and Development in Mexican Communities

SUMMARY The design of an efficient procedure for sampling a rare population can present a challenging task. This paper reviews a variety of methods for sampling rare populations, including screening methods, the use of disproportionate sampling, multiplicity sampling, multiple frames and snowballing. The practical feasibility of the methods is discussed, and examples of applications are given.

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Sampling rare populations

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Dallas W. Anderson

Papers

Sampling rare populations

Sampling Rare Populations